Elevator control for a generator-fed motor control system



May 10, 1966 MORRIS 3,250,72

ELEVATOR CONTROL FOR A GENERATOR-FED MOTOR CONTROL SYSTEM Filed Dec. 5, 1962 convewroowu. 7 1 '16; 8[ LOOP CIRCUIT $32 60L) lloa 28 5 INVENTOR.

AT TORNEYS s 250 972 ELEVATOR CONTROI. For: A GENERATOR-FED MOTOR CONTROL SYSTEM Robert Morris, Bayside, N.Y., assignor to Staley Elevator Company, Inc., Long Island City, N.Y., a corporation of New York Filed Dec. 5, 1962, Ser. No. 242,553 8 Claims. (Cl. 318-141) This invention relates to elevator controls and more particularly to the control of the acceleration (both positive and negative) of the elevator car. The invention relates to apparatus for controlling, an elevator hoist motor and to a method of varying the voltage on the hoist nrotor.

It is an object of the invention to provide improved controls for elevator cars operated with a variable voltage system, also known :as the Ward-Leonard system, that controls the. speed of the hoist motor by changing the voltage supplied to the motor.

It has been the conventional practice to change the hoist motor voltage in steps. With each voltage increase for producing acceleration of the elevator car, there would be a sudden steep rise in the current, followed by a gradual drop as the hoist motor gained speed and increased the back voltage in the circuit.

Steep rise-s or surges of current are objectionable for several reasons. One is that with fast elevators, these surges are likely to exceed the permissible circuit loads; and another objection is that the surges produce irregular acceleration of the elevator car and cause uncomfortable sensations to the occupants of the car.

Another object of the invention is to provide an elevator control circuit with capacitors combined with timers that control the generator field voltage to obtain a smooth current supply in the loop circuit that eliminates current surges but still obtains rapid accelerations and without uncomfortable sensations to the occupants of the car.

Other objects, features and advantages of the invention will appear or be pointed out as thedescription proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIGURE 1 is a diagrammatic view showing an elevator control system made in accordance with this invention;

FIGURE 2 is a chart showing comparative current curves for elevator systems of the prior art and those made in accordance with this invention; and

FIGURE 3 is a graph, similar to FIGURE 2, but showing the comparative results of regenerative braking in elevator systems of the prior art and those made in accordance with this invention.

FIGURE 1 shows an elevator car :having a hoist cable 12 that winds on and unwinds from a drum 14 at the top of an elevator shaft. The drum 14 is driven by a hoist motor 16. The field of the hoist motor 16 is represented by a coil 18. The winding drum 14 has a brake drum to which a brake is applied for holding the drum 14 and for providing auxiliary braking in addition to regenerative braking, which is supplied by the motor 16. There is a brake 22 associated with the brake drum 21 and this brake is released by energizing a solenoid 23 to which power is supplied by normally-open up and down relay switches 24U and 24D.

It will be understood that the operation of the different 3,250,972 Patented May 10, 1966 illustration and the car controls 25 shown on an enlarged scale and outside of the car.

Power is supplied to the hoist motor 16 from a generator 28. The circuit through which this generator is connected with the motor 16 is known as the loop circuit of the system. The hoist motor 16 is regenerative and acts as a brake for producing deceleration of the elevator car; that is, for negative acceleration. The generator 28 is driven by an alternating-current phase-induction motor 30 through a mechanical driving connection 31; and the generator field circuit is indicated by the reference character 32.

The generator field circuit includes a conductor 36 leading to a series of resistors 40-45. One of these resistors, 45, is shown as a variable resistor always in series with the generator field. The other resistors 40-44 are connected in parallel with relay switches. A switch in parallel with resistors 40-41 is indicated by the reference character 8-40; and in similar manner the relay switches in parallel with the resistors 42, 43- and 44 are indicated by the reference characters 8-42, 8-43 and 3-44, respectively.

These relay switches 8-40, 8-42 through 8-44 are normally open. The relay switches have operating coils OCS-40, COS-42, OCS-43 and OCS-44 that close the corresponding relay switches when the coil is energized. Power to energize the coils OCS-42, 0638-43 and OCS-44 is controlled by time delay networks in the circuit ofthe respective coils. There is a different network for each of the relay switches 8-42, 8-43, and 8-44, and these networks are indicated by the reference characters T-42, T-43 and T-44, respectively.

, The elevator controller 25 has a center contact 50 connected with the plus side 52 of a direct current power supply line, and has a movable conductor 53 that is shifted manually and clockwise to connect the contact 50 with a contact 54 to close a circuit through a switch operating coil OC-24U that closes the switch 24U when this coil OC-24U is energized. The energizing of the coil OC-24U also closes switch contacts 24U-RS of a reversing switch 56 in the field circuit of the generator 28. Another switch operating coil OC-60 is in series with the coil OC-24U and, when energized, closes a main power supply switch 60 of the generator field circuit.

Movement of the conductor 53 counter clockwise from the full line position shown in FIG. 1 and into position to touch a fixed contact 62 closes a circuit through an operating coil OC-24D which closes the switch 24D and the contacts 24D-RS of the reversing switch 56. Other contacts 66 and 67 of the controller 25 are used to increase the speed of the car. These contacts 66 and 67 are in parallel to supply power to coil OCS-40 to close contacts 8-400 and to open normally closed contacts 40a and 40b, the purpose of which will be explained later.

Whenever the elevator car 10 starts, the first action of its starting controller 25 is to close the switch 60 in the generator field circuit and to release the brake 22. by closing the relay switch 24U or 24D (depending upon the direction of travel) to energize the solenoid 23. When the elevator car starts, all of the resistors 40 through 45 are in series with the generator field 32 and this supplies voltage at reduced value to the hoist motor 16 for starting. With this invention, however, the resistors 40 through 45 are not relied upon exclusively to control the starting voltage. A bank of capacitors 70 are connected in parallel with the generator field 32 and in series with the resistors 40 through 45; the charging of the capacitors 70 prevents the generator field voltage from building up at an excessive rate. a

When the controller 24 moves into position to close the circuit to either contact 66 or 67, power is supplied to the operating coil OCS-40 of the switch 8-40 and causes the switch 5-40 to close and short-circuit the resistors 40 and 41. The closing of contacts 840C supplies power to network T-42 and to the coil 0SC-42 but the network keeps the current in coil OCS-42 at a low value for a predetermined interval depending upon the time constant of the network and coil. At the end of this interval the coil OSC-42 is fully energized and closes the switch 8-42 to short circuit the resistor 42 and permit the generator field voltage to rise again to a higher value. Coil OCS-42 also closes contacts S420 and supplies power the coil OCS-43 and its associated network T-43. All of the networks T-42-T44 operate in similar manner to short circuit their respective resistors 42-44 and with each network initially energized by the closing of the a switch of the preceding network.

The capacitors 70 have sufficient capacity so that they do not reach the impressed voltage or just about reach it, by the time each network T-42, T-43 and T-44 operates to cause the next resistor 42-44 to be short-circuited so that the voltage in the generator field circuit and the. resulting volt-age in the loop circuit can rise smoothly to a higher value.

When the elevator control circuit is operated to stop the car, the resistors R-40-44 are cut into the generator field circuit by moving the controller 25 out of contact with contacts 66 or 67 and by reverse operation of coil 008-40 and the networks T-42, T-43 and T-44. The

capacitors 70 discharge to eliminate step changes in the voltage supplied to the generator field 32. Somespecial provisions are necessary, however, .to shorten the deceleration period.

One of the special provisions is in the field circuit of the motor 16. 'In that circuit there is the usual standby resistance 74 and a running resistance 76. The standby resistance is short-circuited by contacts 60 which are closed by the coil OC-60 whenever the car is started; and the running resistance 76 is short-circuited by closing of the contacts 40a which forces the hoist motor field the full voltage. The slow-down circuit includes the floor signals in the car and at the floor stations of an automatic elevator system, and the controller 25 of a manual system. This circuitry is not illustrated and it is sufficient to understand that with automatic control the contacts 40a in the motor field circuit and contacts 40b in the generator field circuit, are closed when the automatic controls are operated to slow down the car.

Theshort-circuiting of the running resistance 76 inceases the motor field current, thereby increasing the dynamic effect of the motor 16 which is acting as a generator during slowing down of the car.

Another provision for improved slow-down of the car is a resistor 80 in parallel with the capacitors 70. This resistor 80 is in a closed circuit when normally closed switch contacts 40b are closed. These contacts 40b are opened by excitation of the coil OCS-40, as previously explained. Thus the switch contacts 40b are open when power is being supplied by controller 25 to run the car at full speed. This puts at least part of the resistor 80 in a parallel circuit across the capacitors 70 and across the generator field 32 to obtain a faster slow-down of the car.

In order to obtain smoother starts and slow-downs, it is desirable to have the change in resistance in the generator field circuit vary along a curve which is to some extent exponential instead of a straight-line relation. Therefore, resistance is taken out in larger units in the first steps during acceleration and in smaller steps toward the end of the acceleration period. In deceleration the resistance is put in the circuit in small units at the beginning of the period and in larger units toward the end of the period.

For example, the two resistors 40 and 41 are shorted out simultaneously during acceleration; and the resistor 42, which is shorted out next, preferably has more resistance than each of the resistors 43 and 44. During deceleration, switch contacts S-44, which are closed simultaneously with switch 8-44 by'coil OCS-44 affect the operation; and so do other switch contacts 8-43, which are closed simultaneously with switch 8-43 by 'coil OCS-43, to make the deceleration follow a curve which is more nearly exponential.

The resistors 40-45 are adjustable as indicated by the arrows located along the length of the various resistors. In tracing the groupings or resistors in series with the generator field during acceleration and deceleration, it is useful to identify locations along the circuit by the legends R-l through R-9. In some cases the legend is a location beyond a resistor but in other cases it is the point along a resistor at which a slide wire or other adjustment is located to make only a part of the resistor efiective. I

7 During acceleration of the car, the cutting-out of resistances is according to the following table:

Circuit section Step: cut out by step 1 R-1 t0 R3- 2 -R3 to R-5 3 R-S to- R-6 4 R-6 to R-7 During deceleration of the car, the cutting-in of the resistances is according to the following table: 7

Circuit section Step: cut in by step 1 R-1 to R-Z 2 R3 to R-4 3 R-4to R-5 and R-5 to R-6 4 R-6 to R-7 and R2 to R-3 FIGURE 2 illustrates the principle of operation of the invention and the way in which the elements of the circuit are correlated to obtain fast acceleration of the elevator car without the unpleasant sensation of jerks to the occupants of the car and without successive surges of current in the loop circuit to values in excess of the safe carrying capacity of the motor and the other conducting elements of the loop.

FIGURE 2 shows a curve which represents the operation of. a conventional elevator having variable voltage control for the hoist motor. When power is initially supplied to the hoist motor, the current rises suddenly to a value I-l along a. steep portion 102 of the curve 100. As the speed of the hoist motor increases, the resulting build-up of back voltage causes the loop circuit current to drop, as shown by the portion 104 of the curve 100*.

A resistor is cut out of the loop circuit at the time indicated by the point 106 and these is another sudden increase in loop circuit current to the value I-2 along another steep portion 108 of the curve 100. Again the increase in hoist motor speed, with resulting build-up in the back voltage, produces a reduction in current, as represented by the portion 110 of the curve 100; and the cutting-out of successive resistors produces other surges in current to the values I-3 and I-4.

In the elevator control illustrated by the curve 100, the final surge in current to the value I-4 occurs when the last resistor is cut out and the current then drops to a value I-N which represents conditions with the elevator car moving at full speed and under full load. The sharp rise in current to each of the values I-l through I-4 produces surges in current to the hoist motor with resulting jerks in the movement of the car. This is an uncomfortable sensation for the occupants of the car, as previously explained. Also, each current surge may raise the loop current high enough to operate the circuit breakers of the system and to cause stalling of the car.

FIGURE 2 shows another curve which represents the current supplied to the hoist motor 16 with the control apparatus as shown in FIGURE 1. When power is first supplied to the generator field the increase in voltage is damped by the capacitors 70, as previously explained. This eliminates current surges in the loop circuit.

When the control system of this invention is used, the current supply to the hoist motor is in accordance with the curve 120, and the time of operation of the operating coil OCS-40, and the timers T-42, T-43 and T-44 is indicated on the graph by the points 008405 T-42, T-43 and T-44.

Thus the damping action of the capacitors 70 makes the curve 120 a smooth acceleration curve and the occupants of the elevator car are not conscious of the acceleration. Even if the curve 120 is not as smooth as that shown in FIGURE 2, any ripples in the curve may produce such small surges of current that occupants of the car are not aware of the irregularity in the current increases. Some irregularity is effectively damped by the mechanical inertia of the hoist motor, winding drum and elevator car.

In the correlation represented by the curve 120, the capacitors 70 provide damping-of the current so that the elevator car can accelerate very rapidly without steps in the speed increase and the current in the loop circuit can be high during the entire acceleration but kept to a value not greater than about two and a half times the rated full load of the hoist motor. The timers are adjusted to obtain the smooth curve. The actual correlationis that the charging time for the capacitors 70 is greater than the period of the timer that cuts the next resistor out of the generaor field circuit. Expressed in another way, the time constant of these generator field capacitors and the resistance remaining in series with the generator field at any particular condition of the circuit, should be greater than the time interval before the operation of the next timer.

In practice, this invention has obtained accelerations up to 350 feet per minute Within a single floor spacing and without discomfort to occupants of the elevator car. This example is given merely by way of illustration.

FIGURE 3 shows the operation of a conventional elevator control system with regenerative braking, and the operation of an elevator'system which has regenerative braking but with current damping in accordance with this invention. A curve 100' represents the operation of a conventional elevator. The regenerative current from the hoist motor is represented as a negative current in FIGURE 3 and it has successive current surges to the value I-l through 14. By use of the control apparatus of this invention, a smooth curve 120" is obtained for decelerating the elevator car smoothly and without the jerks represented by the current surges of the curve 100'.

The preferred embodiment of the invention has been illustrated and described, but changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

What is claimed is: I

1. In an elevator control system having a hoistmotor and a genera-tor that supplies power to the motor through a loop circuit, a plurality of resistor units in series in the generator field circuit, and acceleration means for cutting the resistors out of the circuit successively to change the voltage supplied by the generator to the hoist motor, the improvement which comprises capacitors connected in parallel with the generator field and in series with the resistor units, and the capacity and charging time of the capacitors being correlated with the cutting out of successive resistor units to eliminate current surges that produce irregular acceleration of the elevator car and resulting uncomfortable sensations to the occupants of the car, and characterized by the means for timing the cutting out of successive resistor units being a plurality of timers, one for each resistor unit, and switch means by which the than the resistor units are cut out of the 6 timing out of one timer starts the operation of the next timer.

2. In an elevator control system having a hoist motor and a generator that supplies power to the motor through aloop circuit, a plurality of resistor units in series in the generator field circuit, and acceleration means for cutting the resistors out of the circuit successively to change the voltage supplied by the generator to the hoist motor, the improvement which comprises capacitors connected in parallel with the generator field and in series with the resistor units, and the capacity and charging time of the capacitors being correlated with the cutting out of successive resistor units to eliminate current surges that produce irregular acceleration of the elevator car and resulting uncomfortable sensations to the occupants of the car, and characterized by a different switch connected in the circuit of each of the resistor units for cutting that resistor unit out of the generator field circuit, and .a different timer by which each of the different switches is controlled.

3. The elevator control system described in claim 2, characterized by the capacitors being of a capacity which is correlated with the rest of the generator field circuit to continue the charging of the capacitors after the cutting out of each resistance unit for the period required for a timer to cut out the next resistor unit.

4. The elevator control system described in claim 2 characterized by the capacitors having a charging time, with every resistance condition of the generator field circuit, greater than the period of the timer that causes the next change in the resistance of the generator field circuit.

5. In an elevator control system having a hoist motor and a generator that supplies power to the motor through a loop circuit, a plurality of resistor units in series in the generator field circuit, and acceleration means for cutting the resistors out of the circuit successively to change the voltage supplied by the generator to the hoist motor, the improvement which comprises capacitors connected in parallel with the generator field and in series with the resistor units, and the capacity and charging time of the capacitors being correlated with the cutting out of successive resistor units to eliminate current surges that produce irregular acceleration of the elevator car and resulting uncomfortable sensations to the occupants of the car, and characterized by other means for cutting in successive resistor units during slow down of the hoist motor and in timed relation with discharge of the capacitors to obtain a smooth counter voltage for dynamic braking by the hoist motor.

6. The elevator control system described in claim 5 characterized by switches that introduce the resistor units into the circuit during slow down in a different sequence circuit during speeding up of the hoist motor.

7. The elevator control system described in claim 6 characterized by different resistor units being of dif- 'ferent electrical resistance and being correlated in the circuit and with each other to make the voltage curve of the generator field circuit approach that of an exponential function.

8. In an elevator control system having a hoist motor and a generator that supplies power to the motor through a loop circuit, a plurality of resistor uni-ts in series in the generator field circuit, and acceleration means for cutting the resistors out of the circuit successively to change the voltage supplied by the generator to the hoist motor, the improvement which comprises capacitors connected in parallel with the generator field and in series with the resistor units, and the capacity and charging time of the capacitors being correlated with the cutting-out of successive resistor units to eliminate current surges that produce irregular acceleration of the elevator car and resulting uncomfortable sensations to the occupants of the car, and characterized by the capacitors being in a single circuit during slowdown of the hoist motor and only during slowdown.

References Cited by the Examiner UNITED STATES PATENTS 2,313,955 3/1943 Martin et 61. 18729 X 2,641,735 6/1953 Elliot 318-154 X 3,101,438 8/1963 McCall 318 400 FOREIGN PATENTS 511,811 6/1952 Belgium.

1,051,181 1/1954 France.

Re. 16,667 7/1927 Hewlett et a1 318-158 X ORIS L, RADER, Primary Examiner,

1,882,788 10/1932 Eames 318l58 X 1,966,077 7/1934 Nyman 318*428 X 10 "l. LYNCH, Asszstant Exammer.

2,287,835 6/1942 Satterlee. 

1. IN AN ELEVATOR CONTROL SYSTEM HAVING A HOIST MOTOR AND A GENERATOR THAT SUPPLIES POWER TO THE MOTOR THROUGH A LOOP CIRCUIT, A PLURALITY OF RESISTOR UNITS IN SERIES IN THE GENERATOR FIELD CIRCUIT, AND ACCELERATION MEANS FOR CUTTING THE RESISTORS OUT OF THE CIRCUIT SUCCESSIVELY TO CHANGE THE VOLTAGE SUPPLIED BY THE GENERATOR TO THE HOIST MOTOR, THE IMPROVEMENT WHICH COMPRISES CAPACITORS CONNECTED IN PARALLEL WITH THE GENERATOR FIELD AND IN SERIES WITH THE RESISTOR UNITS, AND THE CAPACITY AND CHARGING TIME OF THE CAPACITORS BEING CORRELATED WITH THE CUTTING OUT OF SUCCESSIVE RESISTOR UNITS TO ELIMINATE CURRENT SURGES THAT PRODUCE IRREGULAR ACCELERATION OF THE ELEVATOR CAR AND RESULTING UNCOMFORTABLE SENSATIONS TO THE OCCUPANTS OF THE CAR, AND CHARACTERIZED BY THE MEANS FOR TIMING THE CUTTING OUT OF SUCCESSIVE RESISTOR UNITS BEING A PLURALITY OF TIMERS, ONE FOR EACH RESISTOR UNIT, AND SWITCH MEANS BY WHICH THE TIMING OUT OF ONE TIMER STARTS THE OPERATION OF THE NEXT TIMER. 